Facsimile apparatus



F. c. coLLlNGs, JR 2,376,034

FACSIMILE APPARATUS Filed Nov. 30, 1942 ZSheets-Sheet l May l5, 1945.

ATTORNEY May 15,-1945. F. c. coLLlNGs, JR

` FACSIMILE APPARATUS 2 Sheets-Sheet 2 Filed NOV. 30, 1942 @have 0.3m www. TNQ hmm.

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' l l Ag ATTORNEY Patented May 15, 1945 FACSIMILE APPARATUS Frederick C. Collings, Jr., Riverton, N. J., assig'nor to Radio Corporation of America, a corporation of Delaware Application November 30, 1942, Serial No. 467,423

13 Claims.

v the so-called black and white forms of transmission and reception to the exclusion of the socalled half-tone or modulation method.

In the form of system herein to be disclosed, provision is made for a scanning arrangement for producing signals which are adapted to develop impulse signals in accordance with the shade values on the subject scanned where the impulse signals for one condition of light and shadow are of a ydifferent form or period from the impulse developed to represent a second condition of light and shadow. l

In one form of the arrangement of the invention, it is particularly adapted for the so-calledA tape type of facsimile wherein a record tape is fed through a scanning instrumentality from which, in accordance with the presence or absence of marking indicia on the subject which is scanned, there will be produced'signal energy of two different characteristics, for example, frequency, which will be determined by the presence or absence of marking signals. The system is thus particularly adapted for the transmission of signal energy vto receiving to points where the transmitted signal energy. is particularly related to the scanning,4 of mesmore usual types of scanning where the scanned subject'is more in the nature of a silhouette, so

that distinctions are made between the black and white Values of light and shade.

The invention has been illustrated in'one of its preferred forms by the drawings, wherein:

Fig. 1 is a diagrammatic representation of the transmitter portion of the system; and,

Fig. 2 is a diagrammatic representation of the -recorder amplifier.

The transmitter assembly, as herein incorporated and illustrated, does not show the scanning instrumentality per se, since such devices are well known in the art and any desired form may be used. v 1

One suitable form of transmitter-scanner arrangement which has proven satisfactory in ed to cause a spot of light which is directed upon the prism from asuitable light source of substantially point size, to trace laterally across the subject, and thence, either by transmission of the light through the subject, where the subject is a substantial transparency (as, for instance, a film) the lights and shadows control the current flowing in a photocell or, where light is reflected from the subject in well known manner, where the subject is non-transparent, the reflected light is picked up by a photocell and the current output therefrom is varied in accordance with the variations in light and shadow on the subject.

Referring now to the drawings, and particularly to the scanner and its amplifier, the light as reflected from, or directed through, the subject is caused to reach a photo-tube I I and thereby to vary the photo-electronic current iiowing through it in accordance with the amount of light reaching the cathode I3, so that more or less current flows to the anode I5.

There is connected to the anode I5 a suitable connection to supply a control voltage, measured by the voltage drop occurring across the resistor 21, to the signal or #1 grid 29 of an amplier 3| whose cathode 33 is suitably biased relative to ground 2| by the resistor 35,*and Whose #2 grid 31 derives suitable voltage by way of the resistor 39.' The -#3 or suppressor grid 4I connects to the cathode in theusual manner, while the anode or plate 43 derives its suitable plate voltage from the source connected to the terminal I1 'by way of the load resistor IIS.`

In accordance withsignal energy applied to the control grid 29, it can be seen that illumination of the photo-tube II will cause an increase of current flowing through the tube 3| by reason of the fact that electrons are released from the photo-cathodeA I3, with the result that the control grid 23 becomes slightly more positive with v increased light on the photo-tube.

actual use is that wherein a'prismatic member is rotated at a predetermined speed relative to the subject from which the transmitted signals are to be initiated.` The'prism, as lt rotates, is adapt-v Output'energy from the amplier stage 3l is fed through the coupling condenser l1 to a potentiometer I9 of which the adjustable tap 5I connects to the 'signal control or #l grid 53 of the amplifier tube 55.v The end of the potentiometer 49A opposite that connected tothe condenser 41 connects to ground at 2|.

. resistor 85 l sister 9| in' such a manner the usual cathode load resistor 59 from which output energy is derived by means of the connection provided by conductor 6|, so that, measured in accordance with the current 4flowing through the tube 55, voltage drops will be produced across the cathode resistor 59 connected between the cathode 51 and ground 2 I, with the result that a signal output is derived from the amplifier tube 55 which is a measure of the light impinging upon the photo-tube I I.

'I'he tube 55 has plate or anode voltage supplied to it from a suitable terminal point 63 to which a source of suitable voltage (not shown) is connected. The other connections of the tube are substantially of generally' known form with the #2 grid 65 connected to the anode 61, as illustrated, and the #3 or suppressor grid 69 connected in known manner to the cathode 51. rIhis arrangement provides a low impedance output for controlling the frequency of a local oscillator in a manner which will hereinafter be explained.

For the purpose of adjusting the level of the signals and the signal output from the tube 55, the adjustable contacter 5I of the potentiometer '49 is provided. This sets the level of the output signals which will be measured, and, in accordance with the present description, it will be a measure of the black or marking signals. Output energy from the amplifier tube 55, as derived across the cathode resistor 59 and impressed upon the conductor 6I, is then fed through a coupling condenser 1I in such a manner that signal energy, as it appears in the conductor 13, will be of positive polarity for black or marking picture signals which are impressed simultaneously upon the control electrode 15 of a clipper control tube 11 (which, where desired, need not be a separate tube, as illustrated, but which may comprise but half of the elements within an appropriate tube envelope and have its counterpart formed, for instance, as a detector tube 225, which will hereinafter be referred to).

Signal energy', as it appears at the conductor 13, is also applied simultaneously to one cathode 19 of a double diode tube 9| which will function as a bias and a clipper tube. The cathode 83 of the clipper control tube 11 connects to ground 2| in known manner by way of the bias control of which the variable tapping point 01 is arranged to set the white control level as distinguished from the black control level determined by the adjustable contactor 5| of the potentiometer 49.

Signals, as they are impressed upon the clipper control tube 11 cause, for black in the picture, an increase of current flowing through the tube 11, so that output energyderived from the plate or anode 09 of the tube 11 will produce a voltage drop in the output load resistor 9 I through which resistor plate or anode voltage is supplied to the tube 11 by virtue of the connection established through conductors 93 and 95 of the terminal point 63. As current tends to flow through the tube 11, voltage drops take that increased current flowing in the tube 11 causes the cathode pote tial or the cathode itil to decrease relative to its anode 91..

Signal potentials, as applied through the conductor i3 to the control electrode- 125 are simultaneously applied the cathode 'lilof one half of the diode 8i, so that for signal impulses of positive sign, that is, representing black in the picture, the potential of place across the rethrough the conductor 99 to l 2,376,034 The cathode 51 of the tube 55 is provided withthe cathode 19 relative to its anode |03 will rise to prevent current flow through this half oi' the tube. Under conditions where black in the picture is maintained (that is, a signal of positive sign), the condenser 1| tends to charge.

If now, the signal changes, for instance, to a white signal, so that the impulse is negative in sign, then the potential of the cathode 19, relative to its anode |03, will tend to fall and current will ilow through the half of the tube 0I between the 'cathode 19 and the anode |03. Under such circumstances the cathode 19 tends to go below ground potential when going to white in the picture, and under such circumstances the condenser 1| is discharged by the ow of current within the first half of the tube BI, as above described, and thus prevents overshooting on a change from black to white by way of the low impedance path.

The current flowing in the clipper control tube 11 determines the current iiow through the half of the diode 8| between the cathode IOI and the anode 91. It will be seen that with an interruption of current owing in this half of the bias and clipper diode tube 9| (that is, with white in the transmitted copy), the potential at the control electrode |05 of the control tube |01 will rise relative to its cathode |09 so that the tube I 01 draws plate current. The cathode |09 of this tube connects to ground 2| by the usual cathode resistor III and the by-pass condenser H3.

Under these circumstances, current tends to flow through the tube |01 and thus provides a low impedance path from the Junction |23, through the anode |I1 and cathode |09 of the tube I 01, and thence through the network consisting of the resistor III and condenser IIS to ground at 2| The resistor I i9 connected between the anode I|1 and the control electrode I 05 of the reactance tube |01 is for the purpose of applying negative feedback in the system, and the arrangement provided by the cathode resistor Ill and its shunting condenser II 3, as well as the resistor l 2 l, is somewhat of the nature of a bleedcr combination which causes the cathode |09 normally to be at a positive potential. Normally, a very small current flowing in the diode section between the cathode I0! and the anode 91 will carry the conn trol electrode |05 of the tube |01 beyond its cutoi point, so that the low impedance path from the junction point |23 through the tube |91 and the capacitor H315 removed.

The control tube |01 will, as hereinafter to be pointed out, control the frequency developed by an oscillator tube |29 in a manner later to be described herein. The oscillator tube 82a is adapted to develop a variable frequency, depending upon the action in the tube |01 and whether or not the tube |01 is conducting.

In itsv preferred form, the tube |29 comprises the usual cathode and anode or plate with a plurality of grid or control electrodes. A tube particularly suited for the purpose is one known in the art as the 12SJ7, although other tubes readily may be substituted.

In the arrangement as herein constituted, the oscillatory tank circuit comprises the inductanoe itl having one terminal connected to ground 2| and its other terminal connected to one end of a shunting condenser |33 across which, in parallel, is the capacity combination comprising the condenser I 35 and its trimming shunting condenser |31 which connects on the one hand to the junction point |23, and on thev other hand to the connection point |39 between the inductance |3| and the condenser |33. The operation of this arrangement will later be described.

The end of the inductance |3| which isconnected to ground 2l also connects by way of the coupling condenser |3| to the #2 grid |43 of the tube |29, and the cathode |45 of this tube connects via a resistor |41 to an intermediate point |49 on the lnductance element |3|. Likewise, the #1 grid |5| of the tube |29 connects at a point |53 on the inductance |3|, which` is relatively close to the end thereof, through the usual grid leak resistor |55 and grid condenser |51 to form an oscillatory circuit. In this instance the #2 grid |53 serves generally as the plate or anode element of the oscillator, insofar as the operation of the oscillatory circuit is concerned, and it derives positive potential through the resistor |59 which connects through the conductors 93 and 95 to the positive potential terminal 63. l In the arrangement shown, the #3 grid |6| connects to ground 2| via the conductor |33. I'he plate or anode |65 of the variable oscillator tube |29 derives its plate potential through a pair of resistor elements |61 and |69, of which the .latter connects to the positive terminal 63 via the conductors 93 and 95, and the junction point of the resistors |61 and |69 is connected to ground 2| via the condenser |1 I.

Output energy'from the oscillator tube |29 -is then fed by way of a coupling condenser |13 to a i'llter chain comprising a group of series resistance elements |15, |16, |11 and a terminating resistance element |18 which are respectively lay-passed to ground 2| by the shunt condensers |19, |80 'and |8|.

Under conditions 'when the controlling tube |01 is not drawing current, it will be appreciated that the tube impedance is increased to a maximum and is, in effect, a substantially open circuit, so that under such circumstances the parallel condenser elements |35 and |31 are inef fective to alter the natural oscillatory frequency of the oscillator tube and its oscillatory circuit. This is a state of minimum capacity across the inductance 3| and thus the higher of the two limit frequencies. At times when the control tube |01 is conducting, it will be appreciated that the parallel combination provided by the condensers |35 and |31, together with the low series impedance provided by the control tube |01, forms a parallel combination shunting the condenser |33, in that the cathode |09 of the control tube |01 connects to ground (the con` tance |3| is a maximum and thus the resonating frequency of the tuned circuit is at the lower of the two limiting frequencies.

Thus, it can be seen that for time periods correspondingl to the receipt of positive signals, that is black in the picture as assumed above, the conl denser |33 alone (that is, ignoring, of course, the

inductance element |3|) l will determine the frequency at which the oscillator, |29 develops outn put energy, while for white in the picture (that is, negative impulses in the conductor 13), the frequency of the oscillator will be determined by the value obtained from the combination of the condenser |33 shunted by the series combination of the condenser |35 and its trimming condenser |31 so that, as can readily be appreciated, the oscillator frequency varies from a change between black and white in the picture or scanned subject as it influences the photo-tube For this type of operation, the tube |01 acts as a low resistance path from one side of condensers |35 and |31 to ground when the control electrode |05 of the reactance or control tube |01 is at zero bias. Accordingly, the capacities |35 and |31 in series with such a low resistance will be placed in shunt across the tuning condenser |33. However, when the control electrode |05 of the control tube |01 is biased to a cuto state, the low resistance path herein described is opened, so to speak, and the capacities |35 and |31 return to ground through the high resistance ||5.

Also, for the purpose of developing output energy there is provided a second oscillator tube |83 which 'develops oscillatory energy in a manner substantially similar to that described for tube 29, except that the frequency thereof' remains substantially iixed, except for normally encountered drift, unless crystal stabilization is utilized where desired. y

In the oscillatory tank circuit of the tube |83 there is provided the usual inductance element |85 and the shunting parallel condenser |81, with the connection of the junction point of these two elements to ground 2| being provided.

As was hereinabove explained in connection with the oscillator tube |29, the ground terminal point of the condenser |81 and the inductance element 205, all as above explained in connection with the oscillator |29.

As was also above noted, the #3 grid 201 connects to ground 2| via a conductor 209 and the anode or plate 2|| connects to the conductor 93 via the resistor 2|3 and conductor 2|5, so that positive potential is applied to the electrode member 2||.

For applying a positive potential to the #2 grid |99 there is provided a resistor 2|1 which also connects to the source of positive potential 53 via the conductors 2 l5, 93 and 95.

Again, as explained in connection with the tube |29, the #2 grid |89 serves, insofar as the oscillator is concerned, as a plate element. Output energy derived from the oscillator combination, which, for instance, may be of the order of 50 kilocycles, is then fed by way of the coupling condenser 2|9 and the stabilizing resistor 22| to the control electrode 223 of a detector tube 225. The energy output of the oscillator |29 is f'ed through the stabilizing resistor |18 which is connected with the resistor 22| at the junction point 221 and is also supplied to detector tube 225.'

The output of the voscillator tube |29 varies within a range of the order of about 800 to 1000 cycles, depending upon whether or not the condenser |33 is shunted by the other condensers hereinabove described, andthe normal oscillator frequency of the oscillator 29 is so set that the beat frequency between the outputs of the oscillators |29 and |33 normally varies within a range of about 1000 to 1800 cycles, depending upon the shunted by the by-pass condenser 260.

polarity of the signal pulse in the conductor 13 as supplied by way of the condenser 1|.

Signal energy output from the two oscillators |29 and |83 is, as above stated, applied to the control electrode 223 of the detector tube 225 which is grid biased by means of the resistor 229 connected between the grid or control electrode 223 and ground 2| and suitableA cathode bias is applied by way of the bias resistor 23| which is suitably by-passed for high frequencies by the usual condenser 233.

Plate or anode potential for the detector tube 225 is applied by way of the conductor 93 through the resistor 235, and output from the detector is then fed by way of the coupling condenser 231 to the conductor 239.

The conductor 239 feeds the output energy from the detector 225 to an audio frequency amplifier 24|. The energy output of the detector is passed either through a filtering network represented by the series resistor 243 and the shunt capacitors 245 and. 246 which are connected to ground 2| as indicated, or through a low-pass filter of well known type and conventionally represented at 241, and thence through the volume control resistor 249 to be impressed upon the grid or control electrode 25| of the amplifier tube 24| in accordance with the position of the adjustable contactor 253 of the volume control 249.

In.order to determine whether the energy output of the detector 225 is fed by the tube 24| through the filter consisting of the series resistance 243 and the shunt capacitors 245 and 246, or through the low-pass filter 241, suitable switching elements 255 and'256 are provided' which, when in the lower position, connect the filtering network consisting of the series resistance and shunt capacity, and, when in the upper position, connect the low-pass filter each serially with the fzxrngiductor 239 and the volume control element The cathode 251 of the amplifier 24| is suitably biased relative to ground 2| by means of the cathode bias resistor 259 and may, if desired, be Anode or plate potentials for applying operating voltages to the anode or plate element 26| of the tube 24| are supplied by way of the conductor 263 in known manner, and output energy from the tube 24| is fed by way of the transformer 265 to the output terminals 261 and 269, of which the latter terminal is effectively at ground potential 2|. Y

As was-hereinabove explained, it was possible, where desired, to combine certain of the tubes shown herein separately in single envelopes, and for this purpose it is quite obvious `that the clipper control tube 11 and the detector tube 225 for instance, may be combined within a single amplifier, and, under-such circumstances, a tube of the general type known in the art as the 12SL7GT has proven satisfactory, although naturally other forms of tubes may be used, as desired.

Similarly, the control tube |01 may be combined into a single envelope with the audio frequency amplifier tube 24|, and under such circumstances, a tube of the type known in the art as the 12SN7GT has proven satisfactory, although other forms may be substituted as desired. v

It is of course apparent, in any event, that where combinations of a tube within a single envelope have been made, the tubes are, to all practical intents and purposes, effectively separate tubes, since the electron flow Within'the tubes is in all respects separately controlled and the net effect is a. general reduction in the number of tubes in the system. y

The output terminals 261 and 269 are then connected to energize any desired and suitable form of transmitter arrangement (not shown) for the purpose of transmitting signals to remote points. Under some conditions, when it is desired to monitor the signals appearing on terminal points 261 and 269, without transmission, these terminal points may be connected to suitable input terminal points 281 and 289 (see Fig. 2) from which the energy is passed to a band pass filter 29|. However, under usual conditions, the receiver arrangement particularly shown by Fig. 2 may act as a monitor for the signals transmitted from the transmitter arrangement of Fig. 1 by connecting the terminal points 281 and 289 of the receiver instrumentality to any suitable form of receiver, and tuning that receiver then to the transmitter frequency with which energy from the terminals 261 and 269 is radiated.

'I'he filter 29| may be of any conventional form and type as is well known in the art, and is' accordingly illustrated only in a schematic form.

The output of the filter 29| is then applied to the' primary winding 293 of an input transformer 295 Whose secondary windings 291 and 298 have their innermost terminals connected at a point 299 to which point suitable bias voltage is supplied by way of the conductor 30| which connects to an input bias control resistor 303 having one terminal connected to ground 2| and the other terminal connected to a terminal point 305 at which a positive biasing voltage is applied. The other terminals of the secondary windings 291 and 298 connect to the cathode elements 301 and 308 of a threshhold limiter tube 3| 0 having included therein the usual anode elements 3H and 3|2. This tube may be of the general type known in the art as the 12H6, for instance, and it serves as a usual rectifier device.

The anodes of the tube connect through resistors 3|3 and 3|4, at which the junction point 3|5 is connected to ground 2| by way of a suitable conductor 3|6. In this way it will be apparent that the tube 3|0, in a non-operating state, has its anodes or plates 3| and 3 2 connected to ground 2|, and the cathodes 301 and 306 are then biased slightly positive relative to ground by means of the bias resistor 303.

When signals are received by way of the transformer 295, the negative signals, as impressed upon -the cathodes 301 and 306, cause the tube t0 draw current when the negative signals exceed the predetermined input bias.

The output from the tube 3|0, as it appears across the resistors 3|3 and 3|4, is then supplied by way of the conductors 3|1 and 3|8 to the control electrodes 3|9 and 320 of a suitable peak limiting tube 32|. 'I'his tube may be of the general type known in the art as the 12SC7, although other tubes may be equally well used. y

The cathodes 322 of this tube are connected to ground in well known manner, and the anodes 323 and 324 connect to the outermost terminals of a discriminator of the primary windings 325 of a discriminator transformer 326. The centermost point 321 of the transformer primaries 325 is connected by way of conductor 328 to the bias terminal 305, which thus supplies theplate or anode potential for the peak limiting tube 32|.

Generally speaking, the threshold limiter and peak limiter arrangement, herein described to incorporate the threshold limiter tube 3|0 and the peak limiter tube 32 I, will be seen tobe of the general nature shown and described by Mathes Patent No. 2,267,120 of December 23, 1941, for instance. Thus, it can be seen that the tube 3|0 serves particularly to eliminate or cut out low level noise, and the bias on the tube is set by V means of the input bias control resistor 303 in such a way that any noise introduced into the tube 3|0 could not feed to the peak limiting tube 32|. Similarly, it becomes apparent, from what is shown, that when there is signal energy applied to the tube 3|0 it will function to carry the peak limiting tube 32| negative, so as to cut out the effects of high peaks. The threshold limiting arrangement herein disclosed, for instance, by the tube 3|0, thus is somewhat of a departure from that disclosed by the Mathes patent referred to, although it is to be understood that the general purpose behind the two arrangements is substantially alike.

Output from the discriminator transformer 326 appears in two separate secondary windings 329 and 33| which are suitably tuned to the two beat frequencies hereinabove mentioned to vcorrespond to the frequencies at which the transmitter transmits white and black, for instanceso that one might tune the secondary winding 329 by means of condenser 333 so thatit becomes resonant to a frequency of the order of 1800 cycles, assuming a value as above noted for one extreme beat frequency of the oscillators |29 and |83 respectively.

A suitable damping resistor 335 may be provided across both the secondary coil 329 and the tuning condenser 333. Similarly, with respect to the lower of the two limiting beat frequencies hereinabove assumed as 1000 cycles for the beat between the two oscillators |29 and |83, provision is made for tuning the secondary winding 33| by a condenser 331 across which, where desired, a resistor 339 may be included. y

It will be noted that since the beat frequencies selected are absolute values and normally' not tending in any way to change, the condensers 333 and 331 may, generally speaking, be of fixed value, although it is readily apparent that where the beat frequencies would change to other values, variable condensers may be used for the condensers 333 and 331.

One terminal of the tuned circuits provided by the secondary 329 and the condenser 333 on the one hand, connects to one cathode 348 of a discriminator tube 34|, while one terminal of the other tuned circuit provided by the transformer winding 33| and the condenser 331 connects to the second cathode 342 of the discriminator tube 34|. The outer terminals of the tuned circuits are joined together by the conductor 343 and connect to ground 2| by way of the resistor 344, which resistor may be bridged by the by-pass condenser v345.

One anode 341 of the discriminator tube, which may also be of the general type known as `the 12H6, where desired, connects preferably directly to ground 2| by way of a conductor 348, while the other anode 349v connects to ground by way of both the resistorl 35o and the resister 344. 'rms second anode element 349 also is connected to supply its output by way of a'conductor 35| to a terminal point 352 from which a start-stop relay is controlled. This start-,stop relay is not herein specically shown, but will form the .subject matter of a companion application, Serial No. 467,424, filed Nov. 30, 1942.

Energy in conductor 35| is also supplied to a driver-inverter tube 353 by way of* a resistor 354 which is connected to the control electrode or grid 355 of the driver-inverter tube. The driverinverter tube 353 is, for instance, a tube of the double triode type such, for example, as the 12SL1GT, although other similar type tubes might equally well be used.

Output from the first half of the tube including the control electrode 355, the plate or anode 356 and thecathode element 351 is fed by Way of conductor 358 and resistor 359 to the control electrode 360 of the second half of the tubev compri'sing a cathode 36| and a plate or anode 362, so thatv this output is supplied by way of a direct current connection from the first half of the tube to theisecond half of the tube. Also, a portion of the output of the rst half of the tube v is fed by way of the conductor 363 to the control of the power output tube 368.

.electrode 364 of a. power output tube which is preferably one of the so-called beam power tubes 365, such as the 12A6 for instance.

The output from the second half of the tube 353 as it appears at the anode or plate element 362 is then fed by way of a conductor 366 to the control electrode 361 of a second power output tube 368 of a characteristic generally similar to the tube 365 as will hereinafter lbe explained.

The cathodes 351 and 36| of the tube 353 are suitably biased to ground 2| by way of the biasing resistors 310 and 31|, for instance, of which the cathode 351 is adjustably tapped at-point 312 on the resistor 310.

Connected between the terminals of resistors 310 and 31|, remote from ground, is a third resistor 313. The cathode elements 315 and 316 of the tubes 365 and368 respectively also connect to ground 2| by way of the conductor 311 and the resistor 31| which applies the suitable bias on all the cathodes 36|, 315 and 316 relative to ground.

The output or load resistor 319 for the tube half comprising the cathode 351, the control electrode 355 and the anode 356 of the tube 353 connects between the cathode 315 and the control' electrode 364 of the tube 365, so that voltage drops appearing across the resistor vary the potential of the control electrode relative to its cathode and control thereby the current flowing in the tulbe. Similarly, the load resistor 38| is provided for the half of the tube comprising the cathode 36|, the control electrode 369 and the anode I362, so that voltage drops appearing across the resistor 38| are transferred to the control electrode 361 The cathodes 315 and 316 of the tubes 365 and 368 respectively are suitably by-passed to ground 2| with regard to high frequencies by means of the capacity element 383. The screen electrodes 384 and 385 of the tubes 365 and 368 respectively are supplied with suitable bias voltage by way of a connection to the terminal point 386, as indicated. Suitable plate potential forY the anode or plate elements 388 and 389 is applied by way of the connection through the printer unit coils 392 and 394 and also the resistors 390 and 39| to the positive potential terminal 396.

The beam forming electrodes 393 and 395 of the tubes 365 and 368 connect to the respective tube cathodes in Well known manner. Output energy from .the tubes 365 and 368, as it appears acrossthe load resistors, is applied also to actuate the printer coils 392 and 394 of a'I recorder scanner. The printer coils actuate a presser bar member which is caused to bear upon a recording sheet or strip above which is rotated a suitis not herein illustrated. 'I'he relationship between a single helix and presser bar has been described fully in Reissue Patent No. 20,152 dated October 27, 1936, granted to Charles J. Young, and also Patent No. 2,215,806, where the arrange ment is used for electrolytic recording. In case the arrangement herein disclosed is used for recording with carbon paper or the like upon a record strip, as shown in the Young Reissue Patent No. 20,152, the presser or printer bar is adapted to ibe moved by means of the actuating coils 392 and 394. In case electrolytic recording is depended upon for producing the record at the receiving points, then it is obvious that the current flowing in the output of the tubes 385 and 368 may be caused to vary the current flowing between the presser bar (then tending to rest continuously upon the record strip or sheet and the helix on the cylinder or drum) and the helix, so that the current flowing through the record sheet is varied. Under such circumstances it is, of -course, obvious that the arrangement herein disclosed may be so constituted that the receipt of signals of one frequency may cause current to flow through the record strip, and the receipt of signals of the other frequency may control the interruption of a current.

In the companion case relating to this general arrangement, reference will'be made to the form of control provided from the terminal 352 to a start-stop system by which recording is controlled, and also Iby which the generation of the operating voltages and currents is established and which will include reference to the use of suitable current regulators and the like.

The general arrangement of this present application is particularly directed to the transmitting and the receiving or monitoring equipment, as contrasted with the system by which it is driven and controlled. It will be understood, however, that for complete reference, this application and applicants specification Serial No. 467,424, led Nov. 30, 1942, hereinabove mentioned, should be considered in combination with one another for reference to the complete system. In this connection, it is apparent the modications of this arrangement of the disclosed' device, particularly as to the scanning instrumentality, will be evident from a consideration of what has herein fbeen stated;

Having described my invention, what I claim as new and desire to have protected by Letters Patent is:

1. In a signalling system, an oscillation generator, an oscillatory circuit including inductance and capacity elements associated with-said oscillation generator, a plurality of cascaded thermionic control tubes for said oscillation generator, means for deriving signalling energy occurring at two predetermined energy levels to represent two different signal transmission conditions, means for supplying said signalling energy to said control tubes, means to control thef passage and interruption of current through said control tubes by the signalling energy supplied, saidcontrol tubes being in a different condition of conductivity, reactive means in series with one of said control tubes, said reactive means and said last named control tube being connected in parallel with said oscillatory circuit whereby said generator produces oscillations at twofrequencies determined by the periods of current passage in the control tubes at the two said energy levels.

2. In a signalling system, a thermionic tube and an oscillatory circuit including inductance and capacity elements associated with said thermionic tube whereby said tube develops oscillatory energy, a plurality of cascaded thermionic control tubes for the oscillator tube, means for deriving signalling energy occurring at two predetermined signal levels to represent conditions of signal spacing and signal marking, means -for supplying said signalling energy to said control tubes, means to control the passage and interruption of current through said control tubes by the signailing energy supplied, said control tubes being in a different condition of conductivity, reactive means in series with one of said controltubes. said reactive means and said last named control tube being connected in parallel with said oscillatory circuit whereby said generator produces oscillations at two frequencies determined by the periods of current passage and interruption in tho control tube.

3. In a signalling system, a thermionic oscillation generator, an oscillatory circuit including inductance and capacity elements associated with said oscillation generator, a plurality of thermionic control tu-bes for said oscillation generator, photo-electric means for deriving signalling energy occurring at two predetermined energy levels to represent conditions of spacing and marklng, means for supplying Said signalling energy to said control tubes, means to control the passage and interruption of current flow through said control tubes by the signalling energy supplied, and means operating under the control of saidcontrol tubes for including and excluding a capacitive impedance in the said oscillatory circuit to vary the frequency thereof between two limiting values determined by the periods of current passage and interruption in the control tubes.

4. In a signalling system, a thermionic oscillator, an oscillatory circuit including inductance and capacity elements associated with said oscillator, a. plurality of thermionic control tubes .for said oscillator, means for deriving signalling energy occurring at two substantially different signal levels to represent conditions of spacing and marking, capacitive means for supplying said signalling energy to said control tubes, resistance means to control the ilrst of the said cont trol tubes to set the level at which current flow through the said control tubes is passed and interrupted by the signalling energy supplied, and means operating under the control of said control tubes for changing the impedance of the said oscillatory circuit between two limiting values to generate energy from the oscillator at each of two predetermined -frequencies determined by the periods of current passage and interruption in the control tubes.

5. A signalling system comprising a light translating means to develop energy at each of a plurality oi' dinerent signal levels determined by marking and spacing periods, a thermionic oscillator having included therewith an oscillatory circuit comprising inductive and capacitive impedance elements, a plurality of control tubes connected intermediate the light translating means and the said oscillator, capacitive means for energizing the Vcontrol tubes from the said light translating element to cause said tubes alfrequency varying between plying such signals-to a limiting tubes connected to. receive energy from said diodes, the said diodes serving i for recording the detected energy.

. Y .l 7 trol tube so that etch of said tubes is smultaneously conducting, means for controlling the second control tube by the second diode so that the saidcontrol tubes for changing the oscillatory frequency of the oscillator to one extreme v alue and for changing the oscillatory frequency of the oscillator to the other extreme value for y the opposite condition of current passage and interruption in the control tubes.

6. The circuit claimed in claim comprising,

the second control tube is non-conducting during conducting periods of the second diode, an oscillator, a capacity element connecte'd in the oscillatory circuit of said oscillator, and means provided by said second control tube for including the said capacity element in the oscillatory circuit at time periods when said control tube is operative and excluding the capacity element at in addition, resistance means for controlling the signal level for each extreme condition of output from the light translating means. l

7. The circuit claimed in claim 5 comprising, in addition, a second oscillator of substantially iixed output frequency, means for heterodyning the outputs of each of the oscillators, and means for applying the resultant output signal to a transmission channel. l

8. A signalling system comprising a lightA translating means to develop energy at each of a plurality'of different signal levels determined by marking and spacing periods, a thrmionic oscillator having includedgtherewith an oscillatory circuit comprising inductance and capacity elements, a plurality of control tubes connected in-l termediate the light translating means and the said oscillator, capacitive means for energizing the control tubes from the said light translating element to cause saidtubes alternatively to pass and interrupt a flow of electrical energy in accordance with the alternate conditions of -output from the light translating element, means responsive toone of the states of current passage and interruption in the said control tubes for changing thea lator to one extreme value and for changing, the oscillatory frequency of the oscillator to the other extreme value for the opposite 4condition of current passage and interruption in the control tubes, a second thermionic-oscillatorfor developing a substantially constant output, frequency means for combining the outputs of the two said oscillators Atwo llimiting values frequency range, means for suptransmission channel, a tubes connected in casfrom said transmission in the audible plurality of thermionic cade to receive energy diode` rectiflers and a plurality of thermionic the output to remove low level -noise from thesignals in the transmission channel and the thermionic limiting tubes serving to `eliminate peak noises from the'signals in the transmission channel, a discriminating network connected with theA output of the peak limiting tubes for detecting the signal energy at the two selected frequencies, and means 9. A signalling system comprising a light translating means providing a source 'of signal energy at levels defined by two limital values, a first thermionic 'control tube, a pair of diodes, and a second thermionic control tube, means for applying the signal energy to the first control tube and simultaneously to one of the diodes so that the tubes conduct in opposite senses, means for controlling the second diode from' the first contime periods when .the second tube is inoperative wherebyl the oscillatory frequency is alternatively changed between two limital values.

10. The circuit claimed in claim 9f-comprising. in addition, resistance means for controlling the signal level for each extreme condition of output from the light translating means.

11. The circuit claimed in claim 9 comprising, in addition, a second o scillator of substantially fixed output frequency, means for heterodyning the outputs of each of the oscillators, and means for applying` the 'resultant output signal to a transmission channel.v

l2.'` A signalling system comprising a source .of signal energy, aflrst thermioniccontrol tube, a Pair of diodes, and a second thermionic control tube, means for applying the signal energy to the oscillatory frequency of the oscilto produce a resultant beat channel, said tubes comprising a plurality of vfirst control tube and simultaneously to one of 4that the tubes conduct in opposite the diodes so senses, means for controlling the second diode from the first control tube so that each of said tubes is simultaneously coiiducting, means for controlling the second control tube by the second diode so that the second control tube is non-conducting during conducting periods of the second diode, an oscillator having an oscillatory circuit including impedance elements, and means provided by said secondl control tube for placing the impedance of the oscillatory circuit atone extreme value at time periods when `-said control tube is operative and placing the impedance of the oscillatory circuit -at another extreme value at time periods when thesecond tube is inoperative whereby the oscillatory frequency is alternatively changed between two limital values.

' f 13. A signalling system comprising a scanning element for generating signal energy at levels varying between two limital values, a plurality of thermionic control tubes and a plurality of rectifying tubes, capacitive means for applying the signal energy to one of the said control tubes and. simultaneously to one of the said rectiilers so `that the tubes conduct in ,opposite senses, means for controlling the other of said rectifying v tubes. from the last named control tube so that each of said tubes is simultaneously conducting, means for controlling the second control tube by the second rectifying tube so that the second control tube is non-conducting during conducting periods of the vsecond vrectifying tube,` a vacuum tube oscillator having an oscillatory circuit including inductive and capacitive elements, and means provided by said second control tube for varying the impedance of the oscillatory circuit between` two predetermined values at time periods when said control tube is operativeand at time periods ,when the second tube is inoperative whereby, the oscillatory frequency is alternatively changed between two limital values.

FREDERICK C. COI'.ZIII.INGS,.JR.y l 

